By Gilang Cahya 
In the intricate landscape of biological research, where hypotheses are meticulously crafted and experiments are designed to confirm or refute them, unexpected outcomes can sometimes prove more illuminating than planned results. This principle recently came to the forefront for a collaborative team of scientists from Memorial Sloan Kettering Cancer Center (MSK) and the Icahn School of Medicine at Mount Sinai. Their laboratory investigations, which yielded a surprising counter-response, have opened a promising new avenue for enhancing therapies that utilize small RNAs to target and silence disease-causing genes, with significant potential implications for cancer treatment and a range of other genetic disorders.
The genesis of this discovery lies in a research project aiming to understand the precise mechanisms by which a protein known as ALAS1 facilitates the production of microRNAs, a critical class of small regulatory molecules. The prevailing scientific understanding suggested that ALAS1’s primary function was intertwined with the synthesis of heme, an essential component involved in oxygen transport, energy metabolism, and, as was being investigated, the creation of microRNAs. Led by Dr. Seungjae Lee, a postdoctoral fellow in the laboratory of developmental biologist Eric Lai, PhD, at MSK’s Sloan Kettering Institute, the team embarked on an experiment expecting a predictable outcome: the removal of ALAS1 would lead to a decrease in microRNA levels.
However, the scientific process rarely adheres to preordained conclusions. "Sometimes you do an experiment," explained Dr. Lai, reflecting on the serendipitous nature of scientific inquiry. "You think you’re testing one idea, but when it doesn’t turn out the way you planned, it can lead you to find something else that’s much more interesting." In this instance, the unexpected transpired. Instead of witnessing a decline, the researchers were astonished to observe a significant increase in microRNA levels when ALAS1 was experimentally depleted from the cells. This counterintuitive finding immediately signaled that ALAS1 possessed a regulatory role far beyond its established function in heme production.
The Unveiling of ALAS1’s Dual Nature
This surprising observation prompted a deeper investigation into ALAS1’s multifaceted identity. The protein, known to be a key enzyme in the heme biosynthesis pathway, was now revealed to have an unrecognized "moonlighting" function – a term used to describe proteins that perform multiple, unrelated tasks within a cell. Further experimentation by Dr. Lee and his colleagues confirmed that the depletion of other enzymes within the heme biosynthesis pathway did not elicit the same effect on microRNA levels. This critical distinction solidified the hypothesis that ALAS1’s impact on microRNA production was independent of its role in heme synthesis.
"This told us that ALAS1 has another job outside of helping to make heme, which no one had realized," stated Dr. Lee. Dr. Lai further elaborated, "We can consider this a ‘moonlighting’ function. And here we discovered that ALAS1 has this secret role regulating microRNAs that’s not connected to its normal role in heme synthesis." This revelation, published in the prestigious journal Science, marked a pivotal moment in understanding the complex regulatory network that governs gene expression.
Understanding the Power of Small RNA Snippets
To fully appreciate the significance of this discovery, it is essential to understand the function of microRNAs and their close relatives, small interfering RNAs (siRNAs). Both are remarkably small RNA molecules, typically measuring just 21 or 22 nucleotides in length. Their primary function is to act as molecular guides, binding to specific messenger RNA (mRNA) molecules. This binding event effectively silences the mRNA, preventing it from being translated into a protein. This gene-silencing capability has been a profound revelation in molecular biology, leading to the development of a new class of therapeutic agents.
The scientific community has successfully harnessed this knowledge to create drugs that can precisely target and deactivate genes responsible for various diseases. The landmark approval of patisiran by the U.S. Food and Drug Administration (FDA) in 2018 marked the advent of the first siRNA-based drug, offering a treatment for hereditary transthyretin amyloidosis, a debilitating genetic disorder. Since then, several other siRNA drugs have gained regulatory approval, with many more undergoing rigorous clinical trials. These RNA interference (RNAi) drugs, as they are often called, hold immense promise for treating a wide spectrum of conditions, from rare genetic disorders to more prevalent diseases.
A Collaborative Effort to Validate Findings
The implications of ALAS1’s newly identified role extended beyond the confines of the Lai Lab. Recognizing the importance of validating these findings in a broader biological context, the MSK researchers forged a crucial partnership with specialists in heme regulation and ALAS genes from the Icahn School of Medicine at Mount Sinai. This collaboration, involving Makiko Yasuda, MD, PhD, Robert Desnick, MD, PhD, and postdoctoral fellow Sangmi Lee, PhD, proved instrumental. The Mount Sinai team’s expertise in custom animal models provided the MSK researchers with the necessary tools to extend their observations from cell cultures to living organisms.
These collaborative experiments in mice yielded results consistent with the cell-based studies. When ALAS1 was specifically depleted from liver cells in these animal models, a global increase in microRNA levels was observed. This reinforced the concept that ALAS1 acts as a crucial regulator, or as Dr. Lai described it, a "brake," on microRNA production.
The Therapeutic Horizon: Enhancing siRNA Drug Efficacy
The revelation that ALAS1 acts as a brake on microRNA production immediately sparked a strategic line of inquiry: could manipulating this "brake" be leveraged to enhance the effectiveness of existing and future siRNA-based therapies? The underlying theory is that by reducing the activity of ALAS1, thereby increasing the overall pool of microRNAs, the silencing power of therapeutic siRNAs could be amplified. This enhanced silencing could prove particularly beneficial for targeting genes that are abnormally overactive in disease states, including oncogenes that drive the development and progression of cancer.
While the potential is significant, the researchers acknowledge that this therapeutic strategy is still in its nascent stages. "But we’re not quite there yet," Dr. Lai cautioned. He pointed out that current siRNA drugs face limitations in their efficacy and delivery. For instance, all six FDA-approved siRNA drugs are currently designed to target hepatocytes, the primary cells of the liver. This concentration on liver-targeted therapies is largely due to the liver’s efficient filtering capacity, which facilitates drug delivery.
As a proof-of-concept, the research team demonstrated that they could indeed deplete ALAS1 in mouse liver cells, leading to an increase in microRNA levels. Crucially, this manipulation also enhanced the gene-silencing activity of a model siRNA compound administered to the mice. This finding provides tangible evidence for the potential of this dual-targeting strategy.
A Fortuitous Connection to an Existing Therapy
Adding a remarkable layer of synergy to this discovery is the fact that one of the existing FDA-approved siRNA drugs, givosiran, functions by targeting and turning off ALAS1 itself. Givosiran is used to treat acute hepatic porphyrias, a group of rare genetic disorders affecting heme biosynthesis. The success and safety of givosiran in humans strongly suggest that targeting ALAS1 with siRNA is a viable and well-tolerated therapeutic approach. This opens the exciting possibility of combining givosiran or a similar ALAS1-targeting agent with other siRNA drugs to potentiate their therapeutic effects.
"Since an siRNA against ALAS1 works effectively and safely in humans, this raises the possibility of combining such an agent to enhance other siRNA drugs," Dr. Lai noted. He further suggested that this combination strategy could be broadly applicable to any siRNA therapy, regardless of its specific target.
The implications of making siRNA drugs more effective are far-reaching. Increased efficacy could translate into lower required doses, potentially reducing the incidence and severity of side effects. Furthermore, it could improve the cost-effectiveness of these advanced therapies, making them more accessible to a wider patient population. Perhaps most excitingly, enhanced efficacy might enable siRNA drugs to overcome current delivery challenges and target cell types beyond the liver, thereby expanding their therapeutic reach to a broader range of diseases.
The Enduring Importance of Discovery Science
This breakthrough, born from an unexpected experimental outcome, serves as a powerful testament to the value of curiosity-driven, foundational research. The Nobel Prize awarded in December 2024 to Harvard geneticist Gary Ruvkun, PhD, and Victor Ambros, PhD, for their pioneering discovery of microRNA and its role in gene regulation in the early 1990s, underscores this point. Dr. Lai himself noted his undergraduate thesis research in Dr. Ruvkun’s lab, crediting this experience for igniting his passion for developmental biology and small RNAs.
"Dr. Ruvkun didn’t start out looking for microRNAs," Dr. Lai emphasized. "Like Dr. Ambros, he was investigating the development of nematodes, these tiny worms that live in the soil. And not only did this unveil an entirely new paradigm for how genes are controlled, the field they started eventually resulted in a novel class of human therapies."
The journey from studying simple organisms to developing life-saving human therapies highlights the unpredictable yet profoundly impactful nature of discovery science. In an era where research funding often faces scrutiny and debate, Dr. Lai stressed the critical need for continued support of fundamental scientific inquiry. "When people ask why we’re not spending all of our research dollars directly studying diseases like cancer, why we’re funding research into cells and processes in model organisms like fruit flies, yeast, and bacteria — this is a great example of how discovery science fuels the biggest breakthroughs," he stated. "And I think it is especially critical to keep this conversation active, given how much uncertainty and disagreement there is in society and government about how much to publicly fund scientific research and in what areas. Hopefully, there will be continued support to keep the engine of foundational research strong."
Funding and Disclosures
This groundbreaking research was supported by grants from the National Institutes of Health (R01DK134783, R01-GM083300, P30-CA008748), a Cooperative Centers of Excellence in Hematology pilot grant (10040500-05S1), and a NYSTEM training award (C32559GG).
The researchers have filed a patent application concerning their novel methods for enhancing RNAi therapy efficacy by targeting ALAS1/ALAS2 (WO2024148236A1). Additionally, Drs. Yasuda and Desnick are co-inventors on a patent related to RNAi therapy for acute hepatic porphyrias and report pharmaceutical consulting work.
